1. Field of the Invention
This invention relates to electronic engine control systems, and more particularly to an electronic engine control system capable of controlling ignition timing of an engine having a gasoline injection device.
2. Description of the Prior Art
Heretofore, there have been known engines each provided thereon with a fuel injection device in which a basic fuel injection flow rate is calculated from an intake air flow rate taken into the engine and a rotational speed of the engine. The basic fuel injection flow rate is then corrected in accordance with the condition of the engine in a cold state and during acceleration. A resulting fuel injection signal is fed from an electronic control circuit to a fuel injection device provided on an intake manifold, and a corresponding amount of fuel is injected. In the engine provided with the fuel injection device of the type described, when the throttle valve is fully closed and the engine rotational speed exceeds a predetermined value i.e., engine braking is effected, fuel injection from the fuel injection device is stopped and a catalytic converter is prevented from being heated. Additionally, if fuel injection is directly stopped at the same time the throttle valve becomes fully closed, a shock acts on the vehicle. Hence, a time period is provided between the full closing of the throttle valve and the fuel injection stop.
In controlling the ignition timing of the engine provided with the described fuel injection device, one of the basic ignition advance angles, determined in accordance with the engine rotational speed and the intake air flow rate, which has been previously stored in an electronic control circuit such as a microcomputer, is selected commensurate to the engine rotational speed and the intake air flow rate. A correction ignition advance angle is then determined by intake air temperature, engine coolant temperature and the like and is added to the basic ignition advance--angle so as to determine the optimum ignition advance angle. An ignition signal is then fed from the electronic control circuit to an igniter, whereby a time period for current passage and the ignition timing is controlled.
However, in controlling the ignition timing of the engine provided with the conventional fuel injection device, even when fuel injection has stopped during engine braking and during the time period for awaiting the fuel injection to stop at the very beginning of engine braking ignition timing is controlled by the ignition advance angle determined by the intake air flow rate and the engine rotational speed which tends to lag. Consequently, if the throttle valve is abruptly closed during deceleration, then a gasified fuel-air mixture becomes over-rich upon completion of deceleration. Incomplete combustion of the gasified fuel-air mixture occurs during the combustion stroke due to the relatively retarded ignition advance angle and the slow burning rate of over-rich mixtures to cause after-burns, thereby presenting disadvantages of increased heat loss and possible engine overheating.